MongoDB忽略聚合中使用唯一键的重复文档

db.collection.aggregate([
  {
    $group: {
      _id: "$uniqueField", // 假设 uniqueField 是唯一键
      doc: { $first: "$$ROOT" } // 保留第一个遇到的文档
    }
  },
  {
    $replaceRoot: { newRoot: "$doc" } // 将文档恢复到根级别
  }
]);

db.collection.aggregate([
  {
    $dedup: {
      path: "$uniqueField" // 指定唯一键字段
    }
  }
]);

db.collection.aggregate([
  {
    $lookup: {
      from: "otherCollection",
      localField: "uniqueField",
      foreignField: "uniqueField",
      as: "joinedDocs"
    }
  },
  {
    $unwind: "$joinedDocs"
  },
  {
    $group: {
      _id: "$uniqueField",
      doc: { $first: "$joinedDocs" }
    }
  },
  {
    $replaceRoot: { newRoot: "$doc" }
  }
]);